1. Field of the Invention
The present invention relates to a method of applying electric arc furnace dust in chemical looping combustion process, and particularly a method of applying electric arc furnace dust in chemical looping combustion process without emission of zinc vapor.
2. Description of Related Art
The electric arc furnace dust (EAFD) are particulate matters. These particulate matters are generated in smelting process of an electric arc furnace and are captured by dust collector before the dust of the electric arc furnace is emitted from the high temperature and pressure furnace (or the electric arc furnace) into the air. The EAFD comprises compounds composed of zinc (Zn), manganese (Mn), calcium (Ca), magnesium (Mg), nickel (Ni) and trace lead (Pb). In most countries, EAFD is considered to be a hazardous waste and is present in any setting involving human activity. In recent years, the numbers of steel mills using waste iron and steel as raw materials is increased rapidly in Taiwan. Now, in Taiwan, there are 19 electric arc furnace (EAF) steel plants using waste iron, stainless steel, and alloy of iron as raw materials, and these electric arc furnace (EAF) steel plants have 26 electric arc furnaces. A large quantity of EAFD is generated per tonne of steel produced and around 140,000 tonnes of EAFD is generated each year in the republic of Taiwan. The electric arc furnace dust (EAFD) is dust having a tiny particle size (or particle diameter) and it is (industrial) waste which is easy to be inhaled by humans and accumulated in bodies. Therefore, Taiwan Environmental Protection Administration (EPA) stipulates that the electric arc furnace dust (EAFD) is hazardous and toxic industrial waste so it has to be treated and recycled. Hydrometallurgical method, vitrification method, and pyrometallurgical treatment method are three common methods of treating the electric arc furnace dust (EAFD). In the present work, EAFD were used to test solid fuel combustion, which containing iron, zinc and the others in low concentrations. However, these processes of refining or purifying the electric arc furnace dust (EAFD) are complicated and the cost of these processes is high. Therefore, there is no method capable of recycling the electric arc furnace dust (EAFD) with simpler process and lower cost until now.
Firepower generation is the most extensively used method of electricity generation, but it has a big problem that a serious air pollution is caused by waste gas (including carbon dioxide) produced by firepower generation. Now, the chemical looping combustion process is a more environmentally friendly method among the methods of firepower generation because the chemical looping combustion process has advantages of low exhaust pollution and high power generation efficiency. The chemical looping combustion process is a promising technology wherein two fluidized bed reactors (fuel reactor and air reactor) are utilized to perform reduction reaction and oxidation reaction in turn for firepower generation. Oxygen carrier plays an important role of transmitting heat and oxygen in chemical looping combustion process. Therefore, a thermogravimetric analysis is utilized for reactivity and feasibility evaluation of oxygen carriers before the chemical looping combustion process. After the reactivity and feasibility evaluation, oxygen carriers are modified and prepared according to the result of the reactivity and feasibility evaluation and the performance of oxygen carriers. However, the preparation of oxygen carriers is time-consuming and non-cost-effective. Therefore, if oxygen carriers, which are cheaper and prepared with simpler process, are applied in the chemical looping combustion process, and particularly oxygen carriers prepared by recycling the industrial waste with simple method and process are applied in the chemical looping combustion process, it is helpful to simplify the preparing process of oxygen carriers and to reduce the cost of the preparing process of oxygen carriers. In such a way, the cost of the chemical looping combustion process can be reduced. However, in recent years, all research of the chemical looping combustion process tends to study how to prepare oxygen carriers with natural ore (such as iron ore and ilmenite ore) for low time consumption and low cost. Therefore, there is no technology is developed to apply industrial waste (such as slag, electric arc furnace dust, etc.) in the chemical looping combustion process.